Abstract
In recent years, radio frequency (RF) heating has been explored as a new postharvest pest and pathogen control procedure for agricultural commodities and dry food ingredients. Non-uniform heating and, sometimes runaway heating, have been the major challenges with implementation of this technology. In this study, an experimentally validated computer simulation model was developed to predict the effects of different package geometries, electrode configurations, and use of forced air (60°C) on improving the heating uniformity of raisins treated with RF for insect control. Higher temperatures (60–76°C) were observed in the areas between the edges and corners on the top and bottom layers of the RF treated raisins held in rectangular and cylinder shaped containers, with lower temperatures (40–52°C) observed in the central areas of each layer. The heating uniformity was improved by rounding the corners of the containers and reducing sharp edges on the packages, modifying electrode configurations, and applying forced air after RF heating. These modifications reduced the maximum temperature difference throughout a container of heated raisins to about 5°C. Approximately 356min were needed to raise the raisin temperature in a rectangular container from 23°C to 55–60°C using only forced air at 60°C. In contrast, only 6min of RF heating followed by 10min of forced air treatment at 60°C was needed for a similar filled container to reach a temperature of 55–60°C. Shortening the electrodes length to 4cm shorter than the horizontal dimensions of the rectangular containers also improved heating uniformity. This technique can be easily implemented to improve the uniformity of RF heating in the food industry for the control of insects in packaged dried fruits.
The results in this study provide essential information about the non-uniform heating inside the RF heated materials packed in containers with sharp areas, edges and corners, such as rectangular and cylindrical shaped containers. Rounding the edges and corners in the containers or bending the top and bottom electrodes is key parameters to control the electrical field inside the RF system. This technique can be easily implemented to improve the uniformity of RF heating in the food industry for the control of insects in packaged dried fruits.
•A validated COMSOL model was used to investigate the effects of different factors on the RF heating uniformity of raisins.•Non-uniform heating resulted when treating raisins in packages with sharp corners.•Heating uniformity was improved by reducing corners and edges of package, bending electrodes, and applying hot forced air.•Less time was needed to raise the temp. of the raisins when using RF-forced air (60°C) compared to forced air (60°C) alone.